docs(readme): fix broken documentation links

[rtpHarry]

Sentry have committed the classic sin of updating their documentation url structure and not setting up redirects. Equivalent new urls added into docs.

[rtpHarry]

For the php options, I've updated it to use the public documentation url, as that was what was already in the docs.

However the plugin actually uses a \Sentry\Options object which is documented here and it uses a collection of methods to access the settings rather than the array thats in the public docs.

Perhaps both links should be included in the PR?

[rtpHarry]

Actually, looking into this further, the docs in general are wrong.

There is no array that is returned, its a Options class, so this section actually needs an overhaul:

https://github.com/stayallive/wp-sentry#wp_sentry_options-array

That's beyond just fixing the broken urls, I'm going to open it as a separate issue as its gone midnight here and I'm done for the day.

[stayallive]

Thanks!